Post-Winter Weight Gain

Here’s how to feed your hard keeper once temperatures start rising.
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Post-Winter Weight Gain
Some horses come out of winter a little on the skinny side and require careful diet changes to return to normal body condition. | Photo:

Here’s how to feed your hard keeper once temperatures start rising

If your horse is old, battling a health condition, or a hard keeper, you know how difficult it can be to keep weight on him during winter. It can seem as if he burns through the hay and grain as quickly as you can purchase and toss or scoop it to him. Then, just when you think you cannot handle one more hike in his ration, the temperature climbs, and the grass begins to green. This reprieve might be undoubtedly welcome, but it introduces its own set of considerations; the very forage that brings back his bloom can cause problems, too, from harmful dramatic weight rebounds to metabolic illnesses. So, how can you help him safely regain his pre-winter weight and luster? We’re here to help.

Winter Weight Woes

Fewer feed options, potentially lower-quality hay, and higher calorie expenditure from heat production makes maintaining weight difficult in winter.

Horses respond to cold in a natural setting by eating more to produce this life-sustaining heat. Researchers have discovered that mature horses’ lower critical temperature (LCT), defined as the temperature below which metabolic heat production increases to maintain body temperature, averages around 41ºF (5ºC). Age, body condition, breed, season, and climate all can affect LCT. Scientists (McBride et al.) have suggested that adult horses’ digestible energy intake must increase 2.5% for each degree Celsius below LCT. Other conditions, such as wind and precipitation, can also affect horses’ required energy intake. In fact, Kubiak et al. reported that when exposed to cold and wet conditions, horses’ digestible energy needs can increase to 50% above maintenance requirements (what’s needed when they’re not working).  

For example, an average 1,100-pound mature horse maintenance and in good body condition requires approximately 1,700 kilocalories (kcal, where 1 kcal = 1,000 calories) per day. If temperatures average 30ºF (-5ºC) during the winter, this horse’s requirements increase to 1,955 kcal per day (an adjustment of 42.5 calories per degree for six degrees) to produce heat and stay warm. Once temperatures rise consistently above the LCT, the horse can allocate more calories to building body condition. Therefore, if this horse continues consuming the 1,955-kcal diet during the spring, with the same amount of exercise per day, he should gain weight.

Assessing the Situation

You can assess your horses’ body condition score, or BCS, using a 1-to-9 scale, with 1 as emaciated and 9 as obese (see Nutritionists and veterinarians consider a BCS of 5 ideal for most breeds and ages, though anatomical changes caused by old age (i.e., swayback) or certain diseases might skew this value. So a senior horse might score a 4 and still be in good condition.

Check your horses’ BCS at least every two weeks, especially if they’re seniors or hard keepers, in the winter and spring. Drastic rises or drops over a short period can indicate the horse needs a dietary change, or it could mean that he is ill. Keeping close watch, making adjustments as you go, and calling the veterinarian when you suspect illness will help decrease the springtime weight rebound.

Your goal for a horse who needs post-winter weight-gain should be to increase his calorie concentration without negatively affecting his health and well-being. Many nutritionists estimate that a single change in condition score requires about 16-20 kg, or 36-45 pounds, of weight gain. Therefore, a horse with a BCS of 4 will need to gain approximately 32-40 kg, or 72-90 pounds, to increase to a 6.  

Activity level usually increases with spring as well, so be sure to factor in the added calorie needs that come with it.  

Pasture, Please!

A large majority of the country’s pastures contain cool-season grasses and legumes such as fescue and clover. These become active once temperatures reach 40ºF, but optimal growth takes place when it is 60-80ºF. In the South, warm-season grasses, such as Bermudagrass, flourish when it is 85-95ºF.

Pasture is higher in energy, protein, and, more importantly, digestibility than hay. This is because pasture has higher fractions of acid detergent fiber (ADF), a measure of cellulose and lignin that indicates digestibility, and neutral detergent fiber (NDF), which includes cellulose, hemicellulose, and lignin that predict intake level.  

Horses pastured in the early spring have access to a significantly higher level of nutrition compared to winter. This drastic increase in nutrients, specifically calories, in a highly palatable and digestible form, adds condition and weight to all horses, even seniors with poor dentition. Take care to consider the entire diet, including pasture, when transitioning from a winter to spring ration, with specific considerations for protein, calcium, and phosphorus. Consult an equine nutritionist to advise you on preventing excessive nutrient intake and balancing the ration accordingly.

Continue to monitor the BCS of horses on pasture only, as well, making turnout adjustments to prevent rapid weight gain and obesity. “Just as in rapid weight loss, rapid weight gain is never recommended, as it predisposes horses to other problems such as laminitis and colic, as well as metabolic problems associated with obesity such as insulin resistance,” says Lauren Holtvoigt, DVM, of Prices Creek Veterinary Service, in Lewisburg, Ohio. She suggests introducing horses to spring grass slowly, especially if they haven’t been pastured during the winter, to avoid these dangers.  

Calorie-rich nonstructural carbohydrates (NSC), such as simple sugars, fructans, and starch, are what can tip the scales toward these problems. Up to 66% of the total dry matter of young, immature plants can be comprised of NSC. Horses diagnosed with equine metabolic syndrome, insulin resistance, Cushing’s disease, or that are prone to laminitis cannot tolerate these high sugar and starch levels.  

Holtvoigt says she also wouldn’t recommend NSC-rich spring pasture as the main weight-gain source for severely underweight or very old horses. Additionally, high dietary levels of NSC can sometimes be associated with hyperactivity or a “hot” temperament, yet another reason spring pasture might not be appropriate for all horses.  

The most proactive method for preventing NSC overconsumption is to keep horses off all pasture or reduce the area horses graze by using smaller paddocks. If these are not an option, consider implementing a limited turnout schedule.  

Bridgett McIntosh, PhD, assistant professor and equine extension specialist at the University of Tennessee, studied the circadian and seasonal variation in NSC in pastures while at Virginia Tech. She found that NSC content is highest in cool-season grass pastures when environmental conditions favor rapid growth or when the plant is stressed, such as following a frost.  

“Sugars are the main NSC in spring pasture grasses and are produced through photosynthesis,” she explains. “Therefore, total NSC content is highest on sunny days in the late afternoon and lowest during the overnight hours.” It is also lower on cloudy and rainy days due to reduced sunlight.  

So, what is the optimum turnout time for horses that cannot tolerate high NSC levels yet need to gain weight? McIntosh suggests turning them out during the overnight hours (10:00 p.m. to 6:00 a.m.) and avoiding afternoon turnout (12:00-8:00 p.m.). Remember that even at its lowest point in the early morning hours, NSC content can exceed recommended intake for horses at risk for developing laminitis.  

“It may be necessary to restrict access to pasture altogether when environmental conditions favor accumulation of NSC,” she says. Owners can also use grazing muzzles to reduce forage intake, even in horses with limited turnout.

Post-Winter Weight Gain
Total NSC content is highest on sunny days in the late afternoon and lowest during the overnight hours. McIntosh suggests turning horses out during the overnight hours (10:00 p.m. to 6:00 a.m.) and avoiding afternoon turnout (12:00-8:00 p.m.).

Fat and Fiber for Weight Gain

When pasture is not available or poses the described health risks, fat can serve as an excellent calorie source for weight gain. Fats contain about 2.5 times more calories than carbohydrates and can serve as a concentrated calorie source. Fats also don’t have the metabolic and hyperactive effects that sugar and starch possess.

“Many studies are proving over and over again about the benefits of fats instead of carbohydrates as a calorie source for horses,” Holtvoigt says. “Not only do fats offer a ‘safer’ way to add calories, but fats also provide omega 3s and 6s that can benefit the horse’s hair and hooves.”  

Vegetable fats, such as corn oil, soybean oil, and flaxseed, are common in equine diets. But Holtvoigt cautions that one of fat’s few downfalls is that it can be difficult to store, spoils easily, and can be messy. In addition, Kronfeld et al. found that rapidly introducing fat with a ration can result in greasy feces and increased fecal output, possibly suggesting that horses aren’t digesting all of the fat. Promote proper fat digestion in horses by adding fat to the diet gradually over a period of time.  

As herbivores, horses do require fiber for digestive health, and certain types can be useful for weight gain. Beet pulp, a byproduct of the sugar beet industry, is a highly digestible energy source with a caloric concentration similar to most cereal grains. Researchers have replaced up to 55% of the total diet with beet pulp; therefore, it can be fed safely in fairly large amounts. Hay cubes or pellets are another fiber option and are most commonly available as alfalfa or timothy.  

Take-Home Message

Horse owners have several choices when selecting a post-winter weight gain plan to implement. Naturally, pasture is a calorie-rich option, but it might not be appropriate for all horses; high levels of sugar and starch can be bad news for animals with metabolic disorders. Fat and fiber alternatives abound, including corn oil and beet pulp, which are not associated with negative metabolic affects. Always consult an equine nutritionist or veterinarian with questions about balancing rations for spring (or any) weight gain.


Written by:

Kristen M. Janicki, a lifelong horsewoman, was born and raised in the suburbs of Chicago. She received her Bachelor of Science degree in Animal Sciences from the University of Illinois at Urbana-Champaign and later attended graduate school at the University of Kentucky, studying under Dr. Laurie Lawrence in the area of Equine Nutrition. Kristen has been a performance horse nutritionist for an industry feed manufacturer for more than a decade. Her job entails evaluating and improving the performance of the sport horse through proper nutrition.

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